chemical supply house. For laboratory experiments you will probably use the nitric Saturated Saline & Nitric Acid acid provided from a scientific supply, which is quite expensive compared to the side of There are a number of leaches based upon salt quantity purchase. For example one bottle of water but none have shown the kinetics that nitric acid (71bs) is, at todays cost, $64 and if SSN demonstrates. In one leach the oxida- you bought a 55gal drum the same 71bs of tion potential is created by a combination of acid would cost only $2.10. Salt may be hydrochloric acid and ferric chloride; in an- bought at $ 1.10 per 501b bag at the hardware other leach hydrochloric alone is used and in store, and $25 per ton in truck load lots. To the third electrolytic are employed to create make it simple: check on the commercial molecular chlorine. Pourbaix diagrams show prices in your locale when you calculate that each of these leaches will dissolve gold; leach cost for production runs, In our area it however, the diagrams will not show the could be as low as $0.07 per gallon. kinetic behavior involved (speed of lixiviation). This behavior can only be demonstrated COMPOUNDING THE LEACH by testing and SSN wins hands down. We will look into the behavior of this unique SSN is based upon saturated salt water which means water with every bit of salt that it will leach one aspect at a time. dissolve at normal temperature and pressure. CHEMICALS NEEDED FOR The easiest way to create saturated brine THIS LEACH water is to place approximately 3 lbs of rock salt per gallon of water in a vessel and let it You will need rock salt--not table salt, but dissolve. It helps to stir it occasionally. Just rock salt like you use for water softeners or tc use ordinary tap water for this. Decant the clear ice from the highway. You will neec brine water from any remaining salt (filter if full strength nitric acid (65-70%). Both of there is suspended trash from the rock salt). these may be purchased from an industrial This is the prime liquor and it is ready to go.

It is now time to choose a ratio of nitric acid apparently not accidental for we repeated the to saturated brine water. The low end of the series and the results were the same. reactions is 20 saturated salt water (SS) to 1 nitric acid (N). [SSN=20:1]. At the top end Temperature we have a ratio of 7 SS to 1 N [SSN=7:1]. The top was determined by tests that show when SSN=6:1 the amount of gold dissolved is reduced. In other words there is a point at which the chemistry turns negative. When running these tests we attempted to limit the variables to one and in the following case that variable was acid ratio, A gold plate that was 750 fine and an exposed surface area of 2 square centimeters was used. The 18K gold behaves more like a nugget than pure gold and the set amount of surface defines the other dimension. Temperature was held constant at 31.1 C (88 F)

This graph shows the reaction of SSN with respect to heat. The left column of figures represents milligrams of gold leached from one square centimeter, per hour of exposure. Reading across the bottom of the graph each number is equivalent to a ten degree centiThe left hand column of the graph represents grade increase in working temperature. The the milligrams of gold per square centimeter graph covers 10 C to 90 C. Eighty degrees of gold surface per hour, at 31.1 * C. Across Centigrade (176 F) is the highest practical the bottom is the ratio on nitric acid to Brine. temperature due to volatilization of fluids. Starting at SSN=7:1 on the left and ending The upper arc represents SSN at 7:1 and the with SSN =1:19 on the right. One cannot helplower arc equals SSN at 20:1. The increased but note the sudden rise between 1:16 and chemical activity is a geometric progression 1:13 and again between 1:10 and 1:7. This is by two for each unit of 11 to 13 degrees C.

Molality m mol / kg N I.440E+00 Na 6.000E+00 Cl 6.O00E+0O Pourbaix Diagrams (EpH Diagrams) are an excellent means of visualizing the what, where, and when of chemical reactions. First it would be advantageous to explain a few things for those readers who are not familiar with these diagrams.

Pressure p bar N 1.OOOE+00 Na I.OOOE+00 CI 1OOOE+00 to the left of 0 represent one mole of acid per number, in other words one mole of acid would represent a pH of 0,01 and a second mole would take the pH to -1.0.

The suffix following each chemical species denotes its state of existence. When there is no parenthetic tetter Down the Left side you will see the Eh listed as a the species is a solid crystal. Inmost EpH diagrams voltage. Chemical species by chemical species, the following designations are used: (a) aqueous, (1) element by element; these are the same as you would liquid {such as mercury], (g) gas, (none) solid. find in the electromotive series as listed in CRC, or some other reference book. Usually the diagram is Across the top the first element listed is the element drawn showing from +2.00 to -2.00 volts but we wish of interest and the diagram is used to show its to have a clear view of the area of interest so we ask behavior under the chemical, physical and thermal the computer to draw only that area above 0.00 volts. situation as defined by the temperature (at the top right) and pressure (at the bottom). By performing Across the bottom pH is listed and again we have literally millions of calculations the diagram emerges made a request that instead of the traditional 0 to 14 and we can see the status of (in this case) chlorine (as listing we required an extra two molar on the acid side combined for SSN) at any pH and Eh combination. and only pH 8 on the alkaline side. The minus We have darkened the small area at the upper left so numbers that cationic chlorine will not be overlooked.

Molality m mol / kg CI 4.000E+00 Na 6.000E+00 N 1440E+00

Pressure p bar CI I.OOOE+00 Na I.OOOE+00 N I.OOOE+00

Did you notice that there were chlorine atoms that were no longer associated with sodium chloride? If you did not go back and look at the diagram again.

SSN leach solution contains in this instance about 1.44 molar nitric acid, therefore, you would expect to see a pH 0 when it is measured. This is not the case. Actually the pH reads from pH 0.8 to pH 1.5. So far there is The behavior of nitric acid (70%) in SSN is nothing spectacular in the EpH diagrams, so the topic for this diagram. Nitrogen is there- let's introduce a metal into the solution. fore the element of interest. We are again working at 80C so that the maximum advantage of the chemistry will be well defined. Do not misconstrue that last statement for the reaction is the same at 25 C but the temperature difference will come into play in the next diagram and if the temperature remains the same there is less chance of some one misunderstanding.

Molality m Pressure p mol / kg bar Au l.0OOE*0O Aul J.OO0E+00 N I.440E+00 N I.OOOE+00 Na 6.000E+00 Na I.OO0E+00 CI 1.O0OE+00 CI I.OOOE+00

Chlorine is still the prime element in this EpH diagram, with gold as a secondary element. The SSN leach will convert gold to sodium aurochlorate NaAuCl4 (a) but the energy required shows up at the conventional 1.002 volts. The maximum pH should not exceed -0.8 for good economics. This diagram gives a good comparison with the first one on page 3, but it should be used for comparison of chlorine behavior and not the behavior of gold in SSN @ 80 C. For the true behavior we must consider gold as the primary element. Turn to pagei 6.

Molality m mol / kg I 6.000E+00 1.440E+Q0 a 6.000E+00 Au I.000E+00

Pressure p bar CI 1.0001+00 N 1000E+00 Na 1.000E+00 Au I.000E+00

With gold as the primary element you will note some changes from the previous diagram. The most important is the drop in required ORP (Eh). It was previously running 1.002 volts and has now dropped to approximately 0.890 volts making it much easier to take gold into solution.

This is also the point at which any farther drop in pH will result in a conversion to Au2Oj if the ORP remains high and natural precipitation of elemental gold if the ORP has dropped below the line. From experience; the working window of normal observed pH has been shadowed so that you have an actual visual target to observe. Before we continue with the description of the leaching process we will take a brief look at each of the platinum group metals that are affected.

Molality m mol / kg CI 6.000E+00 N I.440E+00 Na 6.000E+00 Pd I.000E+00 Palladium is by all means the most susceptible of the noble metals that dissolve in SSN leach. In fact the window in which we are working occupies only a small portion of the window of opportunity. This metal will dissolve at any point with a pH below 5.8 and any Eh greater than 380 millivolts. While stripping catalytic converter beads the palladium dissolves with effervescence, turning the solution a light yellow orange. There is no necessity to spend money on heating a leach when palladium is the only element sought.

Pressure p bar CI I.000E+0O N I.000E+00 Na L000E+00 Pd 1.00E+08

Molality m mo! / kg CI 6.000E+00 N 1.440E+00 Na 6.000E+00 Pt I.000E+00

Pressure p bar CI I.000E+00 N I.000E+00 Na I.000E+00 Pt I.000E+00

Platinum shows a higher nobility than palladium but takes less ORP in SSN leach than gold. It needs only about 680 millivolts. Again we have darkened the window through which it appears that we are working. If the Eh remains above 680 platinum will go into solution clear up to a pH of 4.5. Should the Eh drop below the 680 millivolt range and/or the pH exceed 4.5 then the platinum will precipitate.

Molality m mol / kg CI 6.000E+00 N 1.440E+00 Na 6.000E+00 Rh I.000E+00 Rhodium the most prized of the PGE's has a much smaller active window but fortunately it fits within the area in which SSN does its best and most natural work. The ORP is not as high as you would expect but the pH window is quite narrow. Rhodium and alloys of rhodium have leached without incident in our experiments.

Pressure p bar CI I.000E+00 N I.000E+00 Na I.000E+00 Rh I.000E+00

Molality m mot / kg CI 6.000E+00 N I.440E+00 Na 6.000E+00 Ir I.000E+00

Pressure p bar CI I.000E+00 N I.000E+00 Na I.000E+00 Ir 1.000E+00

Iridium offers a very narrow window in which to operate. In fact it is our opinion that any iridium recovered will be happen chance unless the circuit is specifically tailored for that purpose.

There are exceptions, for instance any manganese ore will generate the release of chlorine gas (this is a common way of identifying SSN is the first leach that we have encounmanganese ores). tered which performs better as a stagnant leach rather than an agitated leach. The best results have been derived from a slow trickle A few magnetite samples have given off top to bottom as one would expect from a nitrous oxide for a few minutes and then quit. heap leach. The main difference is that you Remember if there are carbonates in the ore would need weep hoses and a covered heap you will have to pre-leach it in dilute HC1. so that the salt would not build up from Please do not expect any acid based leach to evaporation. When working with one kilo- work with limestone or dolomite. Soils from grams or less a straight forward stagnate dry lake beds may suffer Prag robbing if the clays are bentonitic in nature. If this is the fact leach has given excellent results. there is no leach known that will work.

Tools needed

A bucket , a barrel, a cattle tank, a plastic mortar box, even a plastic lined trench, should do the job. For 4 kilo leaches we use a two inch tower and allow the leach to move through the ground ore by gravity. It is continuously pumped to the top and allowed to circulate. ALL TOOLS THAT ARE USED MUST BE; WOOD, PLASTIC, GLASS OR CERAMIC. SSN has dissolved every metal that we have tried thus far. SSN will destroy your ORP probes by dissolving the platinum side of the probe. It will also destroy the inexpensive hand held meters. They will lock on to a reading and stay there, which gives you a false sense of knowing what is going on. To date the best that we can offer is to keep track of the pH and take it for granted that the ORP is high enough to do the job until we devise a new way to measure it. We might add that the chances of overloading the leach with noble metals is rather remote for its capacity to retain values is tremendous.

Liquid VolumeThe amount of leach liquor to the amount of ore is of no great consequence, just as long as the solution covers the ore. This is true from raw ore to high concentrates. In fact if you use a small surplus of liquid you should be able to draft it off and use it several times before attempting recovery. Be sure to keep the rinse water for recovery, it will serve as dilution water as well as carrying some values that were clinging to the rock surfaces.

RECOVERYFrom our leach liquor we want to recover gold, palladium, platinum & rhodium (possibly iridium).

Here is where the practical method collides head on with environmental considerations. There are two chemicals that will give a straightforward precipitation of the entire group. Unfortunately they are top of the class cancer causing agents and if you order them USE A HOOD you will be obliged to account, in writing as For safety sake always use a hood or leach in well as actually, for every milligram of the the open where fumes may be dissipated. chemical used. Both chrome II sulfate and Most of the ores that we have tested to date do vanadium II sulfate will precipitate all four elements, along with the headaches. not give off noxious fumes.

Formic acid will precipitate gold, palladium & platinum but not the most valuable which is rhodium. The only choice left is cementation (exchange) with a metal lower upon the electromotive series. Zinc is the best choice, the least expensive and the easiest to use. Traditionally lead sulfate is used so as to keep the iron in a reduced state. (This keeps iron from precipitating as Fe203-red iron oxide). This chemical is also a social no-no for it is used by the druggies in making MET and if you order it the FBI will check you out six ways from Sunday. This leaves us an old fashion straightforward zinc and cleanup. Start with the leach liquor diluted with the rinse water (at least two to one rinse to pregnant solution). Place it in a vessel and agitate it well. Check the pH of the solution. It should be somewhere near pH 1.5. If it is not use 10% sodium hydroxide and bring it between 1.5 and 2.0.

When the solution is quiescent pour in the zinc while still stirring it. Most of this zinc is surplus but it is best to be sure that you collect the total values from the solution. Place the solution where it will be warmed but preferably not boiled. ( This will hasten the chemical equilibrium and tighten the floe that forms. Grant about thirty minutes for the reaction to take place and then allow the floe to settle. Carefully decant the spent solution and discard it. Add 5% HC1 to dissolve the hydroxides that formed and part of the excess zinc. Allow the material to settle and decant the greater part of the acid water.

Use 5% to 8% HC1 to dissolve the excess zinc and unwanted metals. All that remain are copper, mercury, gold, palladium, platinum, rhodium and iridium. Filter the solution through a tight filter such as Whatman #50 or a boro-silicate glass such as GF/A. Rinse the filter well and wipe the walls of the precipiWeigh out five and one half grams of zinc tation vessel with apiece of damp filter paper for each liter of solution (21gm/Gal.). For or a second GF/A filter. assay or testing that wouldbe0.55gm/100ml. Divide the zinc into three beakers: 1/41/4- In the absence of copper &/ or mercury the --1/2. filter may be ashed in a lead boat or the GF/ A placed in lead foil. Fold the foil carefully Add water to the first 1/4 of the zinc and stir and cupel it. The resulting bead will be noble well. (This wets the zinc so that there is no metals. Should copper &/ or mercury be gaseous insulation or bubble entrapment to present in small quantities the material, filter insulate the zinc from contact with the preg- and all, should be placed in a crucible, mixed nant solution). Using several short shots of in with flux (any kind) and fired to a button. the well stirred zinc add this to the diluted Cupel the button. leach liquor. Allow five to 10 seconds between each shot. High contaminations of copper and mercury will necessitate that the prepipitates be disWet the second 1/4 batch of the zinc and solved in aqua regia neutralized to pH 7.5-8.0 repeat the last scenario in five to 10 second with sodium hydroxide filtered and acidified shots. If red iron oxide forms just ignore it. with a small amount of hydrochloric acid. Treat this solution as you would any aqua The final l/2ofthezinc should be wetted and regia solution. time allowed for any remaining efferves# cence to subside within the leach liquor. Only sodium hydroxide will drop copper,